1. Field of the Invention
The present invention relates to a fluid injection pump, especially to configure thereof for controlling fluid injection timing and quantity.
2. Background Art
In comparison with a gasoline engine, a diesel engine exhausts gas containing a low percentage of CO and HC, however, containing a high percentage of NOx. Therefore, an important problem of the diesel engine is reduction of NOx contained in exhaust gas. Conventionally, there is a fluid injection pump equipped with a cold start device (hereinafter, “CSD”) for advancing injection timing at clod temperature, serving as an art to keep smooth start of an engine at clod temperature while keeping a low percentage of NOx in exhaust gas. The CSD advances injection timing at cold temperature by controlling a piston to open-and-close a sub port for overflow formed in a plunger barrel.
An example is disclosed in JP 2000-234576A by the same applicant.
The art is applicable to a fuel injection pump as shown in FIG. 20, including a plunger 7 and a plunger barrel 8 with a fuel compression chamber 44 therebetween, wherein plunger 7 is reciprocated so as to suck fuel from a fuel gallery 43 into fuel compression chamber 44 through a main port 14, and to discharge fuel from fuel compression chamber 44 to a connection duct 49 extended to a distribution shaft.
The fuel injection pump has overflow passage generally configured as follows. A fuel drain circuit is formed so as to drain fuel from fuel compression chamber 44 through a sub port 42. The fuel drain circuit includes an open-and-close valve mechanism portion in which a piston 46 fluid-tightly slides for opening and closing sub port 42.
The fuel injection pump is provided with a thermoelement CSD 47 serving as an actuator which actuates according to change of temperature. Thermoelement CSD 47 is constituted by a thermoelement which is extended and contracted according to change of temperature so as to raise and lower piston 46.
The CSD makes piston 46 open sub port 42 when an engine is in the normal temperature, so as to delay fuel injection start timing. The CSD makes piston 46 close sub port 42 when the engine is cold, so as to prevent sup port 42 from draining fuel, thereby advancing the fuel injection start timing.
Due to the configuration, the advance of fuel injection timing for the cold engine prevents misfire so as to optimize cold-temperature start of engine, and the delay of fuel injection timing decreases exhausted NOx when the engine temperature is higher than a certain value, e.g., when the engine normally drives.
In FIG. 21, each of graphs (a) and (b) represents an injected fuel quantity of the fuel injection pump shown in FIG. 20 relative to rotary speed in each of the cold temperature (opening the sub port) case and the normal temperature (closing the sub port) case. It is understood from the graphs that, due to the cold-temperature actuation of the CSD for closing the sub port, the injected fuel quantity is increased at a constant rate regardless of engine rotary speed to be larger than that when the sub port is opened in the normal temperature. The increase of injected fuel may cause increase of noise, overload on an engine, increase of NOx in exhaust gas, and black exhaust gas.
On the other hand, FIG. 22 graphs out fuel timing of the fuel injection pump shown in FIG. 20 relative to pump (engine) rotary speed and to temperature. When the temperature is normal, the CSD does not actuate and the sup port is entirely opened so as to set a late fuel injection timing T1, which is constant regardless of the pump (engine) rotary speed, as a graph (b). Fuel injection timing T1 is determined so as to obtain required effect of reduction of noise and NOx.
When the engine starts in a cold temperature condition where the sub port is entirely closed by actuation of the thermo-sensing CSD 47, an early fuel injection timing T2 is obtained. As the engine rotary speed (pump rotary speed) is increased, the engine is warmed so that the thermoelement of the CSD is gradually expanded, thereby gradually delaying the fuel injection timing. The delay of fuel injection timing effects reduction of black exhaust gas.
In the condition of setting early fuel injection timing T2, an engine can starts smoothly, however, the injected fuel quantity increases, as understood from FIG. 21, thereby causing black exhaust gas and overload on the engine.
In this way, a fuel injection pump provided with the conventional CSD obtains advanced fuel injection timing in compensation for the problems caused by the increase of injected fuel quantity, such as the increase of black exhaust gas and the overload on an engine.